Electrophotographic method and apparatus



Dec. 22, 1910 R. G. OLDEN ELECTROPHOTOGRAPHIC METHOD AND APPARATUS Original Filed June 12. 1964 United States Patent 3,549,251 ELECTROPHOTOGRAPHIC METHOD AND APPARATUS Roger G. Olden, Trenton, N.J., assignor to RCA Corporation, a corporation of Delaware Original application June 12, 1964, Ser. No. 374,747, now

Patent No. 3,442,645. Divided and this application Dec. 16, 1968, Ser. No. 842,034

Int. Cl. G03g 15/00 US. Cl. 355-3 5 Claims ABSTRACT OF THE DISCLOSURE A master electrophotographic record for making copies is applied to the cylindrical surface of a drum. Toner having an electrostatic charge of one polarity are applied to the latent image on the master record to produce a visible image as the drum is rotated. An endless belt of dielectric material for supporting a transfer sheet is charged with an electrostaic charge of opposite polarity to the toner. The transfer sheet adheres to the belt by the resulting electrostatic force which also facilitates image transfer. Pressure is applied between the drum and the belt as the transfer sheet contacts the visible image of the master record. The device for charging the belt is located adjacent to the belt and remote from the contact transfer point between the drum and the belt.

This application is a division of application Ser. No. 374,747, filed June 12, 1964, now US. Pat. No. 3,442,- 645.

This invention relates generally to the field of electrophotography, and more particularly to an improved method of and apparatus for transferring an image on a master electrophotographic record to one or more transfer sheets. The method and apparatus of the present invention are particularly useful or making copies of information from electrophotographic records produced by an electrophotographic output printer of the type pro posed for electronic data processing apparatus.

It has been proposed to transfer the unfused visible image of electroscopic particles on an electrophotographic record to a transfer sheet by placing one side of the transfer sheet against the visible image and exposing the opposite side of the transfer sheet to a corona discharge of a polarity that attracts the electroscopic particles to the transfer sheet. Where the unfused visible image is on a rotatable drum and the transfer sheet is moved against the drum to transfer the image to the transfer sheet, the corona discharge must be applied at substantially the points of contact between the drum and the transfer sheet. The method and apparatus of the invention for the charging and moving of the transfer sheet are even simpler than the prior methods and apparatus.

It is an object of the present invention to provide an improved method of making one or more copies of an image which is on a master electrophotographic record.

Another object of the present invention is to provide an improved method of and apparatus for making a plurality of copies of an image which is on a master electrophotographic record at a relatively higher speed and at a relatively lower cost per copy than has heretofore been possible.

A further object of the present invention is to provide improved apparatus by means of which many prior art electrophotographic machines may be converted to apparatus for producing one or more copies of an image which is on a master electrophotographic record.

Still a further object of the present invention is to pro- Patented Dec. 22, 1970 vide an improved method of copying on transfer sheets of any selected one of many different types an image which is on a master electrophotographic record.

Another object of the present invention is to provide an improved method of transferring an image to a transfer sheet from a master electrophotographic record that is relatively easy to carry out, and improved apparatus by means of which the improved method may be performed efficiently.

These and other objects are attained, in accordance with the improved method of the present invention, in conjunction with an electrophotographic process wherein an unfused image of electroscopic toner particles on a master electrophotographic record is first produced. A sheet of dielectric material is provided with an electrostatic charge of a polarity that will cause the electroscopic particles that form the image to leave the master record. A transfer sheet and the master record are placed in contact with each other with the image against the transfer sheet, and both transfer sheet and master record are stacked on the charged dielectric sheet. Pressure is applied between the master record and the transfer sheet. The electroscopic powder of the image is attracted to the transfer sheet by the charge on the dielectric sheet. The master record is separated from the transfer sheet and the visible images on both the master record and the transfer sheet may be fixed by heat. If more than one copy of the image on the master record is desired, the master record may be redeveloped by applying additional electroscopic toner thereto and the aforementioned meth- 0d can be repeated.

The improved apparatus of the present invention comprises the combination of a dielectric belt with record supporting means, such as a drum, for developing a master record. The dielectric belt is charged at a point remote from the point of transfer of the image from the master record to the transfer sheet. The dielectric belt serves two functions: First, the dielectric belt, when charged, provides efficient conveying means for holding the transfer sheet firmly to it by electrostatic attraction and for moving it into contact with the image on the master record, and, second, the charge on the dielectric belt provides an electrostatic force, other than the corona discharge device, for attracting the electroscopic particles on the master record to the transfer sheet.

The novel features of the present invention, both as to its organization and method of operation, as well as additional objects and advantages thereof, will be more readily understood from the following description, when read in connection with the accompanying drawing in which similar reference charatcers refer to similar parts throughout, and in which:

FIGS. 1, 2, and 3 are schematic sectional views of apparatus for carrying out the steps of charging, exposing and developing a master electrophotographic record in accordance with the improved method of the present invention;

FIG. 4 is a schematic sectional view of apparatus for charging a dielectric sheet in a step of the improved method of the present invention;

FIG. 5 is a schematic sectional View of apparatus for transferring a visible image from a master electrophotographic record to a transfer sheet in a step in the improved method of the present invention;

FIG. 6 is a schematic sectional view of apparatus for redeveloping the master electrophotographic record after a copy has been made in a step in the improved method of the present invention; and

FIG. 7 is a schematic sectional view of one embodiment of improved apparatus for making a plurality of copies from a master electrophotographic record in accordance with the improved method of the present invention.

Referring, now, particularly to FIG. 1 of the drawing, there is shown an electrophotographic record 10, hereinafter called the master record primarily for purposes of identification. The master record 10 may comprise a flexible substrate 11, such as paper, and a photoconductive layer 12, such as photoconductive zinc oxide dispersed in a resin binder.

To produce a visible image on the master record 10, a uniform electrostatic charge is applied to the photoconductive layer 12, in the dark, by a corona discharge device, as shown in FIG. 1. A relatively high voltage, about 6,000 volts, is applied from a power supply 14 between one or more thin wires 15 of a shielded corona dis charge device 16 and a grounded plate 18. The master record 10 is placed on the grounded plate 18. One terminal of the power supply 14 is grounded and the other terminal is connected to at least one wire 15. Depending upon the polarity of the terminal of the power supply 14 that is connected to the wire 15, the master record 10 may be charged either positively or negatively, in a manner known in the art.

The uniformly charged master record 10 is exposed to a light image, as by placing a photographic negative 20 against the master record 10 and exposing the photoconductive layer 12 to a source 22 of light through the photographic negative 20, as shown in FIG. 2. The portions of the photoconductive layer 12 that are exposed to light become conductive and decrease the electrostatic charge in these portions in proportion to the intensity of the light impinging on them. Thus. an electrostatic latent image is formed on the photoconductive layer 12.

The electrostatic latent image can be converted to a visible image by applying electroscopic toner particles thereto, by any suitable means known in the art. Referring to FIG. 3 of the drawing, there is shown an electroscopic developing mixture 24, such as a mixture of toner particles of pigmented shallac, for example, and iron filings applied to the photoconductive layer 12 by means of a magnet 26 to develop the aforementioned latent image thereon. This method of magnetic brush development is described in U.S. Pat. 2,786,439, issued to C. J. Young, on Mar. 26, 1957, for Electrophotographic Developing Apparatus, and assigned to the assignee of the present invention.

Before transferring the unfused visible image on the photoconductive layer 12, an electrostatic charge is applied to a dielectric sheet 28, such as a sheet of insulating plastic material of the polyethylene terephthalate type, of which Mylar is an example. The charge on the dielectric sheet 28 should be of such a polarity that the toner particles are repelled from the master record 10 and driven or drawn towards the transfer sheet. In the arrangement shown in FIG. 5, this means, that for a direct image on the master record 10, the charge on the dielectric sheet 28 should be negative, and, for a reverse image on the master record 10, the charge on the insulating plastic material 28 should be positive. A direct image may be defined as one in which the opaque areas in the photographic negative 20 are duplicated as black areas on the master record 10. A reverse image is one in which the transparent areas on the photographic negative 20 are printed black on the master record 10. Regardless of which method is used, the image on the transfer sheet 30 is always a true facsimile of the image on the master record 10. The electrostatic charge can be applied to the dielectric sheet 28 by means of the corona discharge device 16, energized by the power supply 14, as shown in FIG. 4.

The unfused visible image of electroscopic particles on the photoconductive layer 12 of the master record 10 can be transferred to a transfer sheet 30, such as a sheet of paper, for example, by placing the transfer sheet 30 on the previously charged dielectric sheet 28, and by plac- 4 ing the master record 10 on the transfer sheet 30 with the visible image in contact with the transfer sheet 30. Pressure is then applied between the master record 10 and the transfer sheet 30 by any suitable means, as by a roller 32 adapted to be pushed manually across the top of the master record 10 in the direction of the arrow 34, as shown in FIG. 5. The amount of pressure used is not critical, but there should be enough pressure applied to provide good contact between the master record 10 and the transfer sheet 30. The charged dielectric sheet 28 attracts the electroscopic toner particles of the visible image on the photoconductive layer 12 of the master record 10 and transfers them to the transfer sheet 30, thereby effecting a transfer of the visible image. More than one copy of the visible image on the master record 10 is possible by redeveloping the master record 10, as shown in FIG. 6, as long as the electrostatic latent image is present on the photoconductive layer 12. The redevelopment of the master record 10 shown in FIG. 6 is substantially similar to the original development of the master record 10, as shown in FIG. 3. The number of times the master record 10 may be redeveloped may depend upon the ambient temperature and humidity, the moisture content of the transfer sheet, and the time of each cycle of development.

Referring, now, to FIG. 7 of the drawing, there is shown an embodiment of the improved apparatus for making one or more copies of a visible image on a master electrophotographic record 10a, a portion of a web of electrophotographic record material. The master record 10:: may be similar in composition to the master record 10. The master record 10a is a continuous web of material from which sheets of desired lengths may be cut. The web of the master record 10a is unwound from a supply roll 32, passed over idler rollers 34 and 36, and pulled between a pressure roller 38 and a driven roller 40. The web of the master record 10a is moved over a window 42 of a thin window cathode ray tube TWCRT for exposing the photocpnductive surface 12a of the master record 10a in a manner described by the instant inventor in RCA Review, September 1961, vol. XXII, No. 3. The photoconductive surface 12a of the master record 10a is disposed preferably against the window 42. Where the master record 10a is translucent, its photoconductive surface 12a may be exposed from either surface of the master record. While the thin window cathode ray tube is illustrated herein as means for exposing the master record 10a, any suitable means of electromagnetic radiation known in the art for exposing the master record may be employed.

In order to prevent excessive frictional wear of the thin window 42 by the web of the master record 10a, a web of transparent plastic material 44, having a relatively low coefficient of friction, such as Mylar, is disposed between the master record 10a and the thin window 42 of the cathode ray tube TWCRT. The web of plastic material 44 is unwound from a supply roll 46, passed over an idler roller 48, and pulled by a driven wind-up roller 50. Thus, the master record 10a can be exposed to light from the cathode ray tube through the window 42 and the transparent plastic material 44.

The photoconductive surface 12a of the master record 10a, before being exposed to light, is provided with a uniform electrostatic charge by a corona discharge device 16 disposed adjacent to the master record 10a. The corona discharge device 16 is provided with the usual power supply, not shown for the sake of simplicity. Thus, upon exposure to light from the electron beam at the window 42, an electrostatic latent image is produced on the photoconductive surface 12a of the master record 10a.

After exposure, a suitable length of the web of master record 10a is cut, as by shears 52, and fastened to the cylindrical surface of a rotatable drum 54 by any suitable means, such as by adhesive tape or by suction means (not shown) of the type used in the printing arts. The drum 54 is disposed for rotation about its axis and is rotated by any suitable means, such as a motor (not shown).

The electrostatic latent image on the photoconductive surface 12a of the master record a is developed by moving it over a cylindrical brush 56 disposed to rotate about its axis in a trough 58 of electroscopic developing mixture 24. Any iron filings from the developing mixture 24 remaining on the master record 10a after development can be cleaned up by an electromagnet 60 disposed adjacent to the developed master record 10a on the drum 54. The master record 10a rotates with the drum 54 through any number of desired revolutions, depending upon the number of copies of the unfused electroscopic image thereon to be made.

Means are provided to transport transfer sheets 30 from a stack 62 of transfer sheets to the drum 54 for contact with the image of unfused electroscopic toner particles on the developed (toned) master record 10a. To this end, there is provided a belt 28a of dielectric material, similar to the aforementioned dielectric sheet 28, such as Mylar, for example. The belt 28a is disposed around an idler roller 64 and a driven roller 66 for rotation thereabout. The roller 66 presses the belt 28a against the master record 10a on the drum 54. When an electrostatic charge is applied to the belt 28a, as by a corona discharge device 16a, the belt 28a becomes an efiicient conveyor for a transfer sheet 30 because the latter adheres to the belt 28a by electrostatic attraction. The corona discharge device 1611 is disposed at a point remote from the points of contact 48a between a transfer sheet 30 on the belt 28a and the master record 10a on the drum 54.

To transfer the visible image on the master record 10a to a transfer sheet 30, an electrostatic charge from the corona discharge device 16a is applied to the dielectric belt 28a, and a sheet 30 is placed on the belt 28a. The sheet 30 adheres electrostatically to the belt 28a and is moved thereby into contact with the master record 10a on the drum 54. The drum 54 and the roller 66 are moved synchronously, by any means known in the art. The charge applied to the dielectric belt 28a should be of a polarity opposite to that of the electroscopic toner particles in the developing mixture 24 if a positive image is desired. Thus, when the transfer sheet 30 is brought into contact with the image of electroscopic toner particles on the master record 10a, as at points 48a, the charged belt 28a functions to attract the charged electroscopic particles from the visible image on the master record 10a to the transfer sheet 30. Thus, in addition to serving as a conveyor belt, holding the transfer sheet 30 thereto by electrostatic attraction, the belt 28a also functions as an electrostatic force means to attract electroscopic toner particles wherek by to effect a transfer of the image from the master record 10a to the transfer sheet 30.

The radius of curvature of the roller 66 is small enough so that the transfer sheet 30 cannot follow the belt around the roller 66. For example, when the diameter of the roller 66 is smaller than 1 /2 inches, ordinary paper will not follow a Mylar belt 28a around the roller. Thus, the transfer sheet 30 leaves the roller '66 and falls into a chute 68. A slide 70 at the bottom of the chute 68 is adapted to retain the transfer sheet 30 therein so that it may be exposed to heat from a fuser 72 disposed on one side of the chute 68 and adapted to radiate sufiicient heat to fuse the transferred image on the transfer sheet 30. The sheet 30 is allowed to fall into an exit chute 74 through a slot 76 in the slide 70 after the transferred image has been fused on the transfer sheet 30.

Additional copies may be made of the image on the master record 10a by redeveloping the master record 10a and pressing another transfer sheet 30 into contact with the image of electroscopic toner particles by means of the charged dielectric belt 28a. Thus, by redeveloping the same latent electrostatic image on the master record 10a for each additional copy on the transfer sheet 30 desired, a plurality of copies of an image on the master record 10a may be made. Four copies of good quality have been obtained by transfer from a master record 10a, redeveloping the master record 10a after each transfer and using a master record and a developing mixture of the type described in the aforementioned patent. When the master record 10a is no longer needed, it may be stripped from the drum 54 and allowed to fall onto an exit guide 78. The image on the master record 10a may be fused and kept as a reference, if desired.

It is apparent from the aforementioned description of the method and apparatus of the present invention that the image transferred to the transfer sheet is a mirror image of that on the master record. If the image on the transfer sheet is to be an exact representation of the object that the image portrays, the image on the master record should be a mirror image of the true object. The latter results are easily obtained by using the proper number of lenses and/ or mirrors in a manner well known in the electrophotographic and photographic arts for making a mirror image of a true object on a master record.

From the foregoing description, it will be apparent that there has been provided an improved method of and apparatus for transferring an image on a master record to one or more transfer sheets. Since the transfer sheet can be almost any kind of sheet material, the cost per copy is relatively low. Although the embodiment of the apparatus for carrying out the method is one that is particularly applicable for making copies from master records produced by an electrophotographic output printer of the type proposed for electronic data processing equipment, the improved arrangement of the dielectric belt and the corona discharge device for charging the belt with respect to the means for carrying and developing the master record may be applied to many prior art electrophotographic processing apparatuses. Thus, while only one embodiment of the invention has been described and shown in diagrammatic form, variations in its structure coming within the spirit of this invention will, no doubt, readily suggest themselves to those skilled in the art. Hence, it is desired that the foregoing shall be considered as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for developing a visible image on a master electrophotographic record and for making at least one copy of said visible image on a transfer sheet, said apparatus comprising:

means to apply an electrostatic charge to said record,

means to expose said charged record to a light image to form an electrostatic latent image thereon, a drum mounted for rotation about its axis, means to apply said master record to the cylindrical surface of said drum,

means adjacent to said drum to apply a toner having an electrostatic charge of one polarity to said latent image to produce said visible image on said record when said drum is rotated,

an endless belt of a dielectric material for supporting said transfer sheet,

means adjacent to said belt to apply an electrostatic charge of a polarity opposite to said one polarity thereto whereby said transfer sheet may adhere by electrostatic force to said belt, and

means to apply pressure between said belt and said drum to cause said belt to rotate at the same speed as said drum, whereby said transfer sheet contacts said visible image on said record and effects a transfer of said visible image thereto.

2. Apparatus for developing a visible image on a master electrophotographic record and for making at least one copy of said visible image on a transfer sheet, said apparatus comprising:

means to apply an electrostatic charge to said record,

means to expose said charged record to a light image to form an electrostatic latent image thereon,

a drum mounted for rotation about its axis,

means to fix said master to said drum,

means to rotate said drum about its axis,

means adjacent to said drum to apply an electroscopic toner of particles having an electrostatic charge of one polarity to said latent image to develop said visible image of electroscopic toner particles on said record when said drum is rotated,

a belt of a dielectric material for supporting said transfer sheet,

means adjacent to said belt to apply an electrostatic charge of a polarity opposite to said one polarity thereto whereby said transfer sheet may adhere to said belt by electrostatic force, and

means to move said charged belt with said transfer sheet thereon against said master record on said rotating drum, whereby toner particles of said image are transferred to said transfer sheet, providing said copy of said visible image thereon.

3. In apparatus of the type wherein a master electrophotographic record with a latent electrostatic image on a surface thereof is applied to a rotatable drum to engage electroscopic toner having an electrostatic charge of one polarity, whereby to develop said latent image and to produce a visible image for transfer to a transfer sheet, the improvement comprising:

a belt of dielectric material,

means to support and to press said belt against said drum,

means adjacent to said belt and remote from said drum to apply an electrostatic charge of a polarity opposite to said one polarity thereto whereby said transfer sheet adheres thereto when placed thereon,

means to drive said belt in synchronism with said drum whereby to cause said toner of said visible image to transfer to said transfer sheet, and

means to fix said transferred image on said transfer sheet.

4. In apparatus of the type wherein a master electrophotographic record with a latent electrostatic image on a surface thereof is applied to a rotatable drum to engage electroscopic toner having an electrostatic charge of one polarity, whereby to develop said latent image and to produce a visible image for transfer to a transfer sheet, the improvement comprising:

an endless belt of a dielectric material,

a roller within said endless belt pressing said belt against said drum, means adjacent to said belt and remote from said drum to apply an electrostatic charge of a polarity opposite to said one polarity to said belt whereby said transfer sheet may adhere thereto when placed thereon,

means to drive said roller and said drum to move said belt in synchronism with said drum whereby to cause said toner of said visible image to transfer to said transfer sheet, and

said roller having a radius of curvature such that said transfer sheet leaves said belt in trying to follow said belt around said roller.

5. In apparatus of the type wherein a master electrophotographic record with a latent electrostatic image on a surface thereof is developed with an electroscopic toner comprising toner particles having an electrostatic charge of one polarity, whereby to produce a visible image for transfer to a transfer sheet, the improvement comprising:

a web of a dielectric material,

means adjacent said web to apply an electrostatic charge thereto of a polarity opposite to said one polarity, whereby said transfer sheet can adhere to said web when placed thereon, and

means to press said previously charged web, with said transfer sheet adhered thereto, against said record to cause said toner particles of said visible image to transfer to said transfer sheet.

References Cited UNITED STATES PATENTS 1,482,354 1/1924 Dausmann 128-163 2,576,882 12/1951 Koole 198-41 3,013,878 12/1961 Dessauer 35517(X) 3,216,844 11/1965 King 355--17(X) 3,244,083 4/1966 Gundlach 355-3 3,267,840 8/1966 Tsutomu Honma et a1.

JOHN M. HORAN, Primary Examiner R. P. GREINER, Assistant Examiner US. Cl. X.R. 

